-----Original Message-----
From: Bill Davidson <davidson@sierra.net>
To: Carter <carters@thegrid.net>
Date: Tuesday, August 18, 1998 9:28 AM
Subject: Re: Dometic

>Kit:
>It's hard to stress strongly enough how important the inside fan and
>packing of food for airflow are! (More important the extra fans behind the
>fridge!) You can have a fridge that is working perfectly and still not have
>cold food if there is not adequate air circulation inside the fridge! I
>pack the bottom pretty tight and make it a point to leave the middle of the
>center shelf clear except for the fridge fan. Pay particular attention to
>the use of plastic bags which tend to spread out and form natural blocks to
>airflow!
>
>Regarding adding 12v fans to the back of the fridge:
>First I have to acknowledge Derek Drew because I got some of my ideas and
>much of my inspiration for working on the fans from his article
>"Refrigerator Madness." Thanks Derek! I don't know if the article is still
>available or not. If you want to read it check Vanagon.com or email Derek
>(he posts regularly to 'the list').
>
>I spent A LOT of time figuring this out so I am happy to help others save
>time by sharing my experience. However, I will assume that you will figure
>out some of the details since it would take so long to remember and write
>out. But, if you get stuck on something or just need more information,
>please feel free to email me.
>I checked out the current usage ( with amp meter), the force of airflow (by
>wiring up with alligator clips & blowing each on my face), and the noise
>factor on four fans that were readily available (I did not search far and
>wide for fans). The four fans were: the stock Dometic fan, the Radio Shack
>dc brushless computer fan no. 273-243B, the Fridgemate model A10-2710 Coil
>Fan, and a solar powered fan that Camping World sells (the name of which I
>forgot). I found the Fridgemate to provide the most air movement for the
>amps and it was the quietest of all four fans. It was rather subjective,
>but I felt that each of the Fridgemate fans blew between 1/3 and 1/2 the
>air volume of the stock Dometic fan and used less than 1/3 the amps. I am
>not familiar with the "muffin fans" that you mentioned. If I remember
>correctly the Fridgemate uses about 65mA, the stock Dometic about 220mA,
>and the Radio Shack computer fan about 120mA. I did not make my choice on
>price. I really wanted a quiet, efficient fan system.
>I visualized the airflow path (under the fridge, up the back of the fridge
>through 2 sets of cooling fins, and then out from behind the fridge two
>ways: out the grill behind the top of the fridge and out the grill that
>adjoins the table). Feeling the heat and slow air movement at the grills, I
>felt that the two air exit grills were restrictive and inadequate. So first
>I enlarged the rectangular side grill hole by about two inches toward the
>front of the fridge until it was flush with a horizontal board that is
>beneath the stove burners. I made a new, larger grill, that was more
>permeable to airflow out of flat expanded metal (1/2 inch I think). I
>painted the new grill the light auto flat gray. I bought some 1/8 inch
>black rubber tubing at an auto parts store, slit one wall of it lengthwise
>and fitted it around the edge of the new expanded metal grill. (this keeps
>grill from rattling and looks neat.) Buy taking care with where I cut the
>metal I was able to use the two screws and screw covers from the stock
>grill to mount the new expanded metal grill. Even without extra fans I
>believe that this larger air exhaust vent would improve the cooling of the
>fridge in hot weather.
>The fans were placed as follows:
>One fan about where the original fan was mounted (beneath the lower set of
>cooling fins), but positioned better (in center, from left to right, of
>fins and pointed directly through the lower fins to maximize air flow). The
>second fan was mounted between the lower and upper set of cooling fins
>(careful not to drill through the cooling pipe that travels from right to
>left inside the fridge walls!!). Again positioned more or less in center
>(from left to right) of the lower of the upper set of fins and angled to
>blow air directly through fins (careful not to blow directly on thermo
>switch). The third fan was mounted on the top of the fridge, immediately in
>front of and blowing directly through the enlarged air exhaust vent at the
>side of the fridge. (I put this one on about a 1 inch block of wood to get
>it into the center of the vent hole and wired it with conveniently located
>wire connectors (out of the way of the fan blades) so that it can be easily
>removed when you need to take the fridge out to service it.) This
>arrangement of fans spaces them out along the air flow path and each fan
>adds momentum to the air at crutial points where the fins both need the
>airflow and where the fins slow the air down. The third fan, on top of the
>fridge, also helps to move the hot air that is generated by the propane
>exhaust pipe!
>Some tricks:
>Because the mounts of these Fridgemate fans hold the blades out further
>from the back of the fridge, I was concerned about clearance between them
>and the wall of the van after installation. (It was hard to measure.) Not
>to take chances, I altered the Fridgemate fans by drilling new fan motor
>mount holes in the L shaped mounts such that the result would be the
>Fridgemate blades would be the same distance from the back of the fridge as
>the stock Dometic fan blades. I also eliminated the thermo switches on the
>Fridgemate fans by cutting the white plastic tubes on which they mount to
>about 1/8 inch and using shorter screws. I think I had to reverse the lower
>fan on the mount to get it to position correctly in relation to the cooling
>fins. The fan on top of the fridge also had to be reversed so that the fan
>mount would fit between existing wire strap and the vent hole. Be careful
>when reversing fans on their mounts that you wire them to blow in the right
>direction!! (I wired and tested before reinstalling fridge.)
>All three fans were wired to the original thermo switch after I removed and
>reinstalled it with heat sink compound (from Radio Shack). I also found
>that the original thermo switch mounting bracket bends easily and needed to
>straighten it and take care while remounting that it fit snuggly against
>the cooling fin.
>I also put a very small toggle switch in the circuit for the fan at the
>exhaust grill. I mounted this switch on the expanded metal grill so that I
>could switch this fan off since it is closest to my ears when sitting on
>the back seat. Sometimes it is nice to switch this fan off when I don't
>want to hear it (the other two fans continue to work with this one switched
>off).
>I think that about covers the fans! Good Luck: Bill Davidson
>
>
>
>----------
>> From: Carter <carters@thegrid.net>
>> To: davidson@SIERRA.NET
>> Subject: Dometic
>> Date: Tuesday, August 18, 1998 7:06 AM
>>
>> Hello, Bill
>>
>> I read with interest your series of posts from 8-17-98 re the Dometic. I
>> found them informative and helpful toward adding to my understanding of
>both
>> the theory of operation and function. Thank you.
>>
>> Just before you posted, I pulled mine out on Sunday for inspection and
>> cleaning because I did not think that the propane mode was working. The
>> stock fan worked okay, having tested it with an external battery. I also
>> thought that because this thing is so hard to "observe" or check "in
>place"
>> that the next time I pulled it, I would figure out a way to bench test it
>> which would simply require feeds for the various modes. I would also
>place a
>> table top fan so as to blow on the back of the unit and observe the temps
>> with and without the fan.
>>
>> One thing we do wrong is pack the food in too tight. Hard to resist when
>you
>> have such a small area to begin with but we will now watch it
>nevertheless.
>>
>> I liked what you said re additional fans because it makes sense. The more
>> air transfer, the more efficient the operation, the more cooler it should
>> work. Did you consider using those little muffin fans that are used for
>> cooling computer chips? The reported advantage is less noise (like you, I
>am
>> an anti-noise freak), less amps, and the price isn't bad...around $10
>each.
>>
>> At this point, I am considering adding one or two fans based on your
>> experience. The one behind the side vent is easy enough to figure out,
>but
>> if you posted further details to Roy and could relay same, I would
>> appreciate it. Also I will get one of those battery operated ones for
>inside
>> the fridge.
>>
>> Thanks
>>
>> Kit Carter, 85 Westy GL
>> Central Coast, CA
>>